In recent years, various error correcting techniques for correcting errors of encoded data upon decoding the encoded data have been developed. Also, an error correcting technique having higher error correcting performance is demanded.
The error correcting technique having the high error correcting performance includes, for example, the error correcting technique using LDPC (Low Density Parity Check) codes and the like. An LDPC decoder which performs an LDPC decoding upon correcting errors using the LDPC codes is normally used in combination with an SOVA (Soft Output Viterbi Algorithm) decoder based on a soft decision Viterbi algorithm. Likelihood of soft decision results output from the SOVA decoder are used as error correcting information.
However, even if the encoded data is decoded using the LDPC decoder and the SOVA decoder, if the likelihood lower, the error correcting decoding performance lowers.
Also, it is demanded to enhance the error correcting performance by improving the decoding characteristics of the LDPC decoder in place of development of a new algorithm associated with the error correcting decoding.